The suspects used coded language
and hand-written notes to communicate with the highest-ranking Sicilian mob
boss currently at large, police said in a statement.

Messina Denaro has been sought
since 1993 for planting bombs that killed 10 people in Florence and Milan.

Since 2012, Italy's Carabinieri
police had staked out an isolated farmhouse in southwestern Sicily with
high-tech surveillance equipment. They observed the meetings in which the
mobsters would gather to read Messina Denaro's messages.

To tell one of the group that
there was a message waiting, the owner of the farm would communicate in code
words, like "the sheep need shearing" or the "the hay is
ready," police said.

The messages, known as
"pizzini," were handwritten by Messina Denaro himself, folded into
small balls and wrapped in adhesive tape. They were hidden in the ground under
a rock, and then destroyed after they were read, police said.

Italian Prime Minister Matteo Renzi hailed the
arrests as a blow to the mafia, urging police to continue their work and
"finally capture the most-wanted fugitive."

To avoid police wiretaps and
surveillance, the Sicilian mafia has long used written correspondence instead
of any form of electronic communication.

Denaro's predecessor as boss of
bosses, Bernardo Provenzano, was captured in a farmhouse near his hometown of
Corleone in 2006 with several pizzini on his desk.

The Sicilian mafia, known as Cosa
Nostra, was once Italy's most powerful criminal group but has lost some of its
sway due to the state's success in capturing most of its top bosses.

Meanwhile, across the Strait of
Messina, the Calabrian mafia, known as the 'Ndrangheta, has grown stronger by
becoming one of Europe's biggest smugglers of cocaine from South America.